This invention relates to a drive control apparatus for controlling the driving of a load to be controlled and, more particularly, to a drive control apparatus enabled to drive a load with a simple circuit configuration by performing a backup operation upon occurrence of abnormality of a microcomputer.
Hitherto, a microcomputer fault detection circuit disclosed in JP-A-4-291634 has been provided as a fault detection circuit for detecting a fault of a microcomputer. FIG. 4 shows the configuration of this microcomputer fault detection circuit.
As shown in FIG. 4, a conventional microcomputer fault detection circuit 101 comprises a microcomputer 102, whose fault is to be detected, a reset IC 103 with a watchdog function, which receives a clock signal from this microcomputer 102 and outputs a reset pulse upon occurrence of abnormality, and a detection circuit 104 adapted to output an alarm when reset pulses, the number of which is equal to or more than a predetermined value, are detected.
In the microcomputer fault detection circuit 101 of such a configuration, the microcomputer 102 outputs clock signals, which have equal durations, to the reset IC 103 with the watchdog function at nearly constant periods when normal program processing is performed according to a program loaded thereinto. Further, when some abnormality occurs in the microcomputer 102 and thus the supply of clock pulses is ceased, the reset IC 103 with the watchdog function, which receives the clock signals, outputs a reset pulse every predetermined time period until the supply of clock signals is resumed.
Incidentally, in the case that the microcomputer 102 runs away and the supply of clock signals is completely stopped, the reset IC 103 having the watchdog function continues to output reset pulses. In the detection circuit 104, the reset pulses charge a charging capacitor. When a charging voltage reaches a predetermined level, the detection circuit 104 outputs an output signal as an alarm.
However, although the conventional microcomputer fault detection circuit 101 detects an occurrence of a fault of the microcomputer 102, the circuit 101 cannot drive a load controlled by the microcomputer 102.
Therefore, in the case that the microcomputer 102 is an ECU (Electrical Control Unit) mounted on a vehicle, an additional backup circuit should be provided by using a wire harness so as to drive a load, which is controlled by the microcomputer 102, by performing a fail-safe operation when abnormality occurs in the microcomputer 102. Thus, the conventional microcomputer fault detection circuit 101 has problems in that the cost thereof increases, and that the weight of the vehicle increases.
The invention is accomplished in view of the foregoing circumstances. Accordingly, an object of the invention is to provide a drive control apparatus enabled not only to detect an occurrence of abnormality of a microcomputer with a simple circuit configuration, but to drive a load controlled by the microcomputer.
To achieve the foregoing object, according to the invention, there is provided a drive control apparatus (hereunder referred to as a first drive control apparatus of the invention), in which a drive circuit performs a drive control operation by performing switching of on/off of a load to be controlled, according to setting of an output port of a microcomputer. This drive control apparatus comprises a drive signal supply unit for generating, when a power-supply voltage is supplied thereto, a drive signal, which is used for driving a load from this power-supply voltage, and for supplying this generated drive signal to the output port of the microcomputer.
This first drive control apparatus of the invention can drive a load by performing a fail-safe operation upon occurrence of abnormality of a microcomputer with a simple circuit configuration that eliminates the necessity for providing an additional backup circuit by using a wire harness.
An embodiment (hereunder referred to as a second drive control apparatus of the invention) of the first drive control apparatus of the invention further comprises a drive signal stop unit for stopping, when the power-supply voltage has a value that is equal to or less than a predetermined value, the drive signal supply unit from supplying the drive signal.
According to the second drive control apparatus of the invention, a load to be imposed on a battery at the time at which the power supply voltage lowers, for example, at an engine start can be reduced.
An embodiment (hereunder referred to as a third drive control apparatus of the invention) of the first or second drive control apparatus of the invention further comprises a drive signal delay unit for delaying the drive signal outputted by the drive signal supply unit.
This third drive control apparatus of the invention can prevent a malfunction of the load at power-on thereof and ensure the safety of a worker.
According to an embodiment (hereunder referred to as a fourth drive control apparatus of the invention) of the first, second or third drive control apparatus of the invention, the drive signal outputted by the drive signal supply unit is supplied to a plurality of drive circuits.
The fourth drive control apparatus of the invention can drive a plurality of loads with a simple circuit configuration, in which a plurality of drive circuits are provided, upon occurrence of abnormality of the microcomputer.